pass-by-value

Here's an obvious situation that must arise all the time for people: struct Foundation { var columns : [Column] = [Column(), Column()] } struct Column : CustomStringConvertible { var cards = [Card]() var description : String { return String(describing:self.cards) } } struct Card {} var f = Foundation() for var c in f.columns { c.cards.append(Card()) } That code is legal but of course it has no effect on f , because var c is still a copy — the actual columns of f are unaffected. I am not having any difficulties understanding why that happens. My question is what people generally do about it.

I'm wondering the best form for my constructors. Here is some sample code: class Y { ... } class X { public: X(const Y& y) : m_y(y) {} // (a) X(Y y) : m_y(y) {} // (b) X(Y&& y) : m_y(std::forward<Y>(y)) {} // (c) Y m_y; } Y f() { return ... } int main() { Y y = f(); X x1(y); // (1) X x2(f()); // (2) } From what I understand, this is the best the compiler can do in each situation. (1a) y is copied into x1.m_y (1 copy) (1b) y is copied into the argument of the constructor of X, and then copied into x1.m_y (2 copies) (1c) y is moved into x1.m_y (1 move) (2a) result of f() is copied into x2.m_y (1

I made a simple program in c++ to compare performance between two approaches - pass by value and pass by reference. Actually pass by value performed better than pass by reference. The conclusion should be that passing by value require fewer clock-cycles (instructions) I would be really glad if someone could explain in detail why pass by value require fewer clock-cycles. #include <iostream> #include <stdlib.h> #include <time.h> using namespace std; void function(int *ptr); void function2(int val); int main() { int nmbr = 5; clock_t start, stop; start = clock(); for (long i = 0; i < 1000000000;

This question already has an answer here: Is JavaScript a pass-by-reference or pass-by-value language? 29 answers Suppose I have an object as: var obj = { len: 4, bred: 5 } Now suppose I assign this object to a variable x as var x = obj; . As far as I understand it, it creates a copy of obj and assign that copy to x  — that is pass by value. Now If I change a property of x then it changes that property of the obj object too. E.g. x.len = 99 Then both obj.len and x.len become 99 . On the other hand consider this scenario: var r = 2, s = 3, t = 4; s = r; s = 88; Now r is passed by value to s

My program: #include<stdio.h> #include<conio.h> char* str(char*src);\\declared as function global main() { char src[40]="hello"; clrscr(); puts(src); str(src);\\ function called puts(src);\\does not put changed string? getch(); return 0; } char* str( char *src) { src="readers";\\changing my source string<--is it changes??? return src;\\returning source sting } output: hello hello Why is src not becoming "readers" ? In your code, src="readers"; is wrong. You have to try like strcpy(src, "readers"); The reason is, C uses pass by value while passing function parameters. So, src here is passed by

My little sample code Function AddNr(ByRef x As Integer) As Integer x = x + 2 AddNr = x End Function Sub test() Dim ana As Integer ana = 1 AddNr (ana) MsgBox ana End Sub should output 3 but outputs 1. To be more specific the ana variable is not modified after the call to the AddNr function. My environment is Microsoft Visual Basic 6.5 inside Excel 2007. That should be: AddNr ana That is, no brackets. From Microsoft Help: Remarks You are not required to use the Call keyword when calling a procedure. However, if you use the Call keyword to call a procedure that requires arguments, argumentlist